BRIdging Disciplines of Galactic Chemical Evolution (BRIDGCE) Consortium 2021-2024

"How did the Universe begin and evolve" is one of the three science challenges identified in the STFC Astronomy Programme. We address this question by modelling physical processes from the micro (nuclear, stellar) to the macro scales (galactic, cosmological), studying the ionising and chemical feedback from stars and the wider context of galaxy formation.

The BRIDGCE consortium is a multidisciplinary collaboration between nuclear, stellar and extra-galactic astrophysicists, which aims to achieve a comprehensive understanding of the evolution of the Universe from the era of reionisation up to now, using chemical elements as fingerprints of the physical processes that occur in stars and galaxies. Elements heavier than helium are produced in stars and supernovae on different timescales, and the stellar populations and interstellar medium within galaxies keep a record of star formation and chemical enrichment histories of galaxies. Therefore, it is also possible to constrain galaxy formation theory from the observed elemental abundances, and to do this more accurately we need to understand stellar and nuclear Astrophysics. Moreover, the discovery of gravitational waves (GW) has opened a new window to the Universe, allowing us to observe the formation of black holes and neutron stars more directly than ever before. GWs can provide independent new constraints on stellar winds, evolution, and stellar deaths via black hole remnants, and the seeds of super-massive black holes in galaxies.

The development of high-performance computing enables us to study the theory of stars and galaxies self-consistently: we simulate how stars lose mass via stellar winds prior to supernovae explosions (Project-1); we simulate the full evolution of stars in one-dimension (1D) and compute 3D scans of their interiors (Project-2). Furthermore, by combining stellar evolution and nucleosynthesis to galactic dynamical evolution, we reproduce the entire chemodynamical history of local dwarf galaxies (Project-3) and of the Milky Way (Project-4). Our research addresses some of the key questions of 21st century Astronomy: How black holes and neutron stars are formed (Projects 1 & 2)?, How many GW events will be detected in future missions?, and How we can trace the evolution of the Universe from GWs (Project-5)?

Nuclear data (nuclear reaction rates in particular) are a key input for stellar evolution models since nuclear reactions provide the energy that powers stars. This information determines stellar lifetimes and the composition of their ejecta. Stars provide important feedback into galaxies through the light they radiate, their powerful winds and explosions, and all the chemical elements they produce. The outputs of stellar models are thus key ingredients for galactic chemical evolution models. These models follow successive episodes of star formation and trace the history of the enrichment of the elements. The model predictions can then be compared to observations of stars, stellar populations, and the inter-stellar medium that carries the chemical fingerprints of the cumulative chemical enrichment that preceded their birth. Comparison to observations can thus constrain both the galactic and stellar properties. Finally, most stars are not born on their own, but may instead evolve interacting with a companion. Although this has been known for decades, the impact of binarity on galaxy evolution is poorly known.

In the BRIDGCE 2021-2024 grant, our galaxy experts will explore this new scientific problem together with our stellar experts. Our consortium project applies innovative techniques across different disciplines and tackles this challenge through 5 projects corresponding to very different physical scales: stellar envelopes (Project-1), stellar cores (Project-2), local dwarf galaxies (Project-3), the Milky Way (Project-4), and the Universe as a whole (Project-5). These impact many areas of Astrophysics as well as Cosmology & Nuclear Physics.

Societal Impact including Public Engagement

BRIDGCE science spans enormous scales from the very small (nuclei) to the very large (stars, galaxies, and the Universe). Furthermore we utilise state-of-the-art technology, from international accelerator facilities such as CERN to study nuclear reaction rates to large scale high-performance computing facilities such as DiRAC to generate evolving simulations of astronomical objects like stars and galaxies. Our consortium thus has a unique opportunity for societal impact and building public support for science by capturing the imagination of non-scientists, addressing life's big questions and enthuse the next generation of scientists. Our impact is achieved in several ways: public engagement, teacher training, interactions with the media and promoting equality and diversity.

All of our institutions have been regularly running public engagement events, namely at Armagh Observatory and Planetarium (AOP), University of Hertfordshire Observatory at Bayfordbury, Keele Observatory, Keele Stardome inflatable planetarium, and the National Schools Observatory (NSO) at LJMU. Murphy is co-leading the STFC Public Engagement Sparks award Remote^3. All of our institutions also have dedicated links with local schools. Two particularly effective routes are specialised teacher training days which are organised regularly at York in conjunction with the National STEM Science Learning Centre, and Hertfordshire's full-time Outreach and Public Engagement (OPE) officer whose work is integrated with the SEPnet and Ogden Trust OPE programmes.

All of BRIDGCE members are active public speakers and we frequently appear in the media. For example, Kobayashi featured on ANA flight entertainment to show her galaxy simulations. Laird spoke on BBC Radio 4, Murphy frequently speaks at science events, and Vink regularly speaks to the Dublin and Belfast amateur societies.

Societal Impact and Evaluation Plan

A coordinated approach to OPE will be undertaken within BRIDGCE, highlighting the synergies between computational hydrodynamics, nuclear and stellar astrophysics, and Big Data exploitation. In particular, we will develop new animations from our large-scale simulations to: engage the public in a fun and interactive way, enhance the content of outreach at our respective institutions and to inspire the next generations of scientists. Our team members will then engage with the public via the various channels available at our institutions listed above (observatory visits, teacher training, media interactions, stardome sessions). We will design our engagement activities with an interactive two-way communication framework in mind and assess the effectiveness of our impact using participants evaluation questionnaires. Furthermore, in cooperation with ChETEC and IReNA networks, we will contribute the results of our research projects (e.g. stellar yields, GCE models) to a periodic table phone App, which will include the origin of the chemical elements.

Economic Impact

While blue skies sciences do not have direct economic impact, the team members we train often enter highly-skilled jobs. A strong societal and economic impact of our consortium is thus in the form of enhancing the UK human capital via frontiers scientific research. Furthermore, Hirschi has set up in the framework of the ChETEC COST Action support for inter-sectoral activities that would emerge from scientific projects or support for technological input into research project via a dedicated working group (no 4), and Ryan is translating astrophysical expertise directly into biomedical imaging research (e.g. https://www.nature.com/articles/s41598-019-55769-5).